Method and apparatus for rerouting a connection in a data communication network based on a user connection monitoring function

ABSTRACT

A method and apparatus for rerouting connections in a data communication network based on detection of faults or other undesirable characteristics using a user connection monitoring function is presented. After a connection is established that is managed by a control plane, the status of characteristics of the connection is monitored using a user connection monitoring function. In one embodiment, the user connection monitoring function includes the use of operation and management (OAM) cells. When the status of one or more of the selected characteristics being monitored is determined to be unacceptable, control plane rerouting of the connection is initiated. Selected characteristics that may be monitored using the user connection monitoring function include, for example, continuity, data corruption, data loss, latency, and misinsertion of data. The reroute initiated in response to the unacceptable characteristic may be a hard reroute or a soft reroute.

FIELD OF THE INVENTION

The invention relates generally to data communication and moreparticularly to a method and apparatus for rerouting a connection in adata communication network based on a user connection monitoringfunction.

BACKGROUND OF THE INVENTION

Data communication networks are commonly used to transport data betweenend users. In many cases, virtual connections are established betweenparticular end users to facilitate the transport of data. In someinstances, these connections are switched virtual connections, orswitched virtual circuits, whereas in other cases, the connections aremore permanent in nature.

Some types of connections are established with the capability ofself-rerouting if faults or other problems arise which by inference meanthat the flow of data over the connection will be negatively affected(e.g. A physical link failure stops data flow on all connections on thatlink). One such type of connection is a soft permanent virtualconnection (SPVC), which is a type of connection often employed inasynchronous transfer mode (ATM) networks. SPVCs provide an advantage inthat the network manager does not have to interact with every switchalong the path of the SPVC, but rather merely configures the endpointsand the network is able to select an appropriate path over which to mapthe SPVC. SPVCs provide an advantage in that they can quickly recoverfrom faults that impede the flow of data.

In prior art systems, reroutes of SPVC connections are typicallytriggered upon detection of control plane faults (e.g. signaling linkfailure) or physical layer faults (e.g. physical link failure).Detection of such faults is used to infer a fault in the user plane ofthe SPVCs that are controlled by the signaling link or riding on thephysical link. Similarly, the lack of such control plane faults andphysical layer faults is used to infer the well-being of the user planeconnections that they manage. However, the actual status of the userplane connection itself at the ATM layer, or at a similar layer in otherprotocol networks, is not used in such prior art systems as a potentialtrigger for rerouting an SPVC. This is undesirable, as the well being ofthe user plane connection itself is what subscribers, or users of thenetwork, perceive. In some instances, the user plane may be experiencingproblems that are not evidenced by faults detectable in the controlplane or physical layer entities. As such, a user plane fault may nottrigger a reroute while still causing problems.

Therefore, a need exits for a method and apparatus for reroutingconnections that is capable of detecting user plane faults that may notbe detectable using control plane or physical layer monitoring.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a flow diagram of a method for rerouting a connectionin a data communication network in accordance with a particularembodiment of the present invention;

FIG. 2 illustrates a block diagram of a communication system withinwhich connection rerouting based on user plane fault detection can occurin accordance with a particular embodiment of the present invention; and

FIG. 3 illustrates a block diagram of a network controlled by a networkmanager, where reroutes within the network may be triggered based onfaults detected using a user connection monitoring function inaccordance with a particular embodiment of the present invention.

DETAILED DESCRIPTION

Generally, the present invention provides a method and apparatus forrerouting connections in a data communication network based on detectionof faults or other undesirable characteristics using a user connectionmonitoring function. After a connection is established that is managedby a control plane, the status of characteristics of the connection ismonitored using a user connection monitoring function. In oneembodiment, the user connection monitoring function includes the use ofoperation and management (OAM) cells. When the status of one or more ofthe selected characteristics being monitored is determined to beunacceptable, corrective action such as control plane rerouting of theconnection is initiated. Selected characteristics that may be monitoredusing the user connection monitoring function include, for example,continuity, data corruption, data loss, latency, and misinsertion ofdata. The reroute initiated in response to the unacceptablecharacteristic may be a hard reroute or a soft reroute.

By utilizing the user connection monitoring function, a user'sperspective on the connection is an additional indicator used fordetermining whether or not corrective action on the connection isrequired. Because the user may perceive data flow problems that are notascertainable based on control plane or physical layer fault detectionschemes used in prior art systems, utilization of the user connectionmonitoring function for monitoring the connection ensures that such userplane problems are detected. As such, a user plane problem that could beperceived as troublesome to a user but not recognized in prior artsystems is readily ascertained and corrective action can be taken toalleviate the problem. By combining the user plane monitoring with priorart connection-monitoring techniques, a more complete connectionmonitoring technique is achieved.

The invention can be better understood with reference to FIGS. 1-3. FIG.1 illustrates a flow diagram of a method for rerouting a connection in adata communications network. The data communication network may supporta variety of protocols, including asynchronous transfer mode (ATM),multi-protocol label switching (MPLS), Frame Relay, or other cell- orpacket-based data transmission protocols that may rely on virtualconnections, switched paths, or similar constructs to transport data. Inother embodiments, networks that utilize wavelength switching maybenefit from the techniques described herein.

The method of FIG. 1 begins at step 102 where a connection isestablished in the data communications network. The connection ismanaged by a control plane, which may be a signaling plane that utilizesprotocols such as private network-to-network interface (PNNI). Theconnection may be a switched connection, such as a soft permanentvirtual connection (SPVC), or a switched virtual connection (SVC). Inother embodiments, paths such as MPLS or LSP types of paths may be the“connections” that are monitored and maintained.

Once established, the connection may be monitored using conventionalcontrol plane and physical layer monitoring schemes that are capable ofdetecting control plane faults and physical layer faults. However, basedon the teachings of the present invention, such monitoring techniquesare supplemented through the use of a user connection monitoringfunction. At step 104, at least one selected characteristic of theconnection is monitored using such a user connection monitoringfunction. The user connection monitoring function monitors theconnection from the same perspective as a user making use of theconnection. As such, if the user data is not being properly transmittedalong the connection (possibly due to faults), the monitoring occurringbased on step 104 will detect such a lack of proper data flow.

The monitoring performed at step 104 may include monitoring specificselected characteristics as illustrated at step 106. At step 106,characteristics such as continuity, data corruption, data loss, latency,and misinsertion of data are monitored. Continuity monitoring willdetermine if the data flow along the connection is interrupted such thatdata flow is essentially halted. Data corruption monitoring maydetermine whether or not an unacceptable percentage of the data cells orpackets being transmitted along the connection are corrupted while intransit. Data loss monitoring can be used to determine whether or not anunacceptable percentage of the data being transmitted along theconnection is lost while in transit, where data loss differs from datacorruption in that no data is received at the destination portion of theconnection when data loss occurs, whereas corrupted data is received atthe destination when data corruption occurs.

Monitoring the latency of data along a connection can be used todetermine whether or not an unacceptable amount of time is required fordata to traverse the connection from the source node within the networkto the destination node. For example, a user may pay for a specific typeof service over the connection, where such a service guarantees acertain maximum latency for data traffic. If this guaranteed latency isexceeded, rerouting of the connection may be desirable in order toprovide the level of service guaranteed to the user. Misinsertion ofdata may occur when data intended for one connection is mistakenlyinserted onto another connection such that it does not arrive at theproper destination. It should be noted that a number of other monitoringfunctions not described in detail herein may be used to determine whenan unacceptable condition has arisen on a connection such that reroutingor other corrective action is desirable.

Within an ATM system, the monitoring performed at step 104 may includethe use of OAM cells as illustrated in step 108. At step 108, OAMfunctionality is utilized to monitor the one or more selectedcharacteristics for the connection. OAM functionality is known in theart. Utilization of OAM functionality includes configuring an OAM cellsource, which generates OAM cells, and an OAM sink, which extracts OAMcells from a data stream. The OAM source generates the OAM cells andperiodically injects the OAM cells into the user data stream such thatthe OAM cells traverse the network in the same manner as user data. Uponreceipt at the node that includes the OAM sink, the OAM cells arerecognized and extracted from the data stream for analysis.

OAM cells used for monitoring continuity checking may be injected intothe user data stream either on a periodic basis independent of the flowof user data, or may be injected only when there is insufficient userdata being transmitted to allow for continuous monitoring of continuityalong the connection. In order to validate continuity, an OAM sink atthe destination node of the connection may monitor the connection forany type of data flow, where such data flow may include standard userdata or OAM cells that may be injected merely to ensure that some levelof data flow is provided along the connection. If no flow of data isdetected by the node that includes the OAM sink (i.e. no cells are beingreceived within the node), a loss of continuity along the connection hasoccurred. In some instances, a configurable threshold level may beestablished for such a loss of continuity detection, such that if nocells corresponding to the connection are received for a time periodthat exceeds a predetermined time period, a loss of continuity (LOC)condition may be detected.

The type of OAM cells used to monitor continuity may be referred to asOAM continuity checking (CC) cells. In addition to OAM CC cells, OAMperformance monitoring (PM) cells may be utilized to monitor othercharacteristics of the connection. Thus, whereas OAM CC cells merelyindicate whether or not continuity is present along the connection, OAMPM cells can be used to verify the actual performance of the user planeconnection (in addition to verifying continuity). For example, OAM PMcells may be used to verify that a certain level of user planeperformance that has been guaranteed to a user is being provided. Inperformance monitoring, configurable thresholds may exist for thevarious characteristics that are monitored by OAM PM cells, whereas anunacceptable level on any particular characteristic may be used todetect a situation that requires a reroute in order to ensure that theuser's needs are adequately met. Thus, a plurality of selectedcharacteristics may be monitored, where if a particular propertycorresponding to one of these characteristics exceeds a correspondingpredetermined threshold for that characteristic, a reroute may betriggered.

Because different thresholds may be appropriate for differentconnections, flexibility may be achieved by ensuring that the variouspredetermined thresholds associated with various characteristics can beconfigured. Such configuration may occur at the instantiation of theconnection, or may be a dynamic process that allows for suchpredetermined thresholds to be modified after the connection has beenestablished such that dynamic alternation of the connectioncharacteristics can be achieved.

At step 109, it is determined whether or not the status of one or moreof the selected characteristics being monitored is unacceptable. If not,the method returns to step 104 and the monitoring function continues. Ifit is determined at step 109 that the status of one or more of theselected characteristics is unacceptable, the method proceeds to step110 where control plane rerouting of the connection is attempted.

As described above, the determination at step 109 that the status of theselected characteristic is unacceptable may include determinations suchas those illustrated in steps 112 and 114. At step 112, the status ofthe continuity is determined to be unacceptable when loss of continuityis detected for a time period that exceeds a predetermined threshold. Atstep 114, the status of the selected characteristic is determined to beunacceptable when a property of the selected characteristic exceeds apredetermined threshold established for that characteristic.

The initiation of control plane rerouting performed at step 110 mayinclude performing a soft reroute at step 116 or performing a hardreroute at step 118. A hard reroute implies that the old connection isreleased while (or before) the new connection is established such thatthe old connection is abandoned irregardless of the performance obtainedthrough the use of the new connection. As such, a hard reroute mayresult in the establishment and initial use of a new connection thatprovides even worse performance than the old connection which wasabandoned based on its inability to support the data flowcharacteristics required.

In the case of a soft reroute, which may also be referred to as a“bridge and roll”, an evaluation of the new connection may be performedbefore the old connection is abandoned and the data flow is reroutedover the new connection only if its characteristics are better thanthose of the old connection. Whether a hard reroute or a soft reroute isperformed at step 100 may be based on the type of characteristic thathas been determined to be unacceptable at step 109. For example, in thecase of a loss of continuity, a hard reroute is likely to produce animproved new connection as the loss of continuity on the old connectionessentially makes the old connection useless. However, if the selectedcharacteristic deemed unacceptable at step 109 is associated with theperformance of the connection, such as the latency along the connection,a soft reroute may be preferable in order to ensure that the newconnection provides better latency performance than the old connectionbefore the old connection is abandoned in favor of the new connection.

Although the techniques illustrated in FIG. 1 have been describedprimarily with respect to an ATM data communication network, it isapparent to one of ordinary skill in the art that similar techniques maybenefit other types of data communication protocols. For example, a datacommunication network may support MPLS data communication, where thecontrol plane in such an MPLS system may employ signaling protocols suchas CR-LDP or RSVP, while relying on a routing protocol such as OSPF orIS-IS. In such a communication network, the connection may be a labelswitched path (LSP) that is monitored from a user perspective in orderto ascertain whether or not the LSP is providing the level of serviceagreed upon by the network manager and the user relying on the LSP. Thespecific user plane monitoring technique relied upon in MPLS may be assimple as a ICMP Echo (“ping” type) communication or MPLS-specificinband management packets, which may be analogous to OAM CC cell trafficin an ATM network, or it may be more complex such that functionalitysimilar to that provided by OAM PM cells is achieved. Similarly, thesetechniques may also be applied to switching of wavelength paths.

In communication networks that support yet other protocols, the specifictype of user connection is dependent upon the type of protocol utilizedwithin the network, and the monitoring technique used to detect faultswithin the user plane may either be built into the particular protocolbeing supported or may be generated specifically to provide such userplane verification functionality. As is apparent to one of ordinaryskill in the art, the particular monitoring function may be specificallytailored to suit the characteristics to be monitored such that themonitoring activities are efficient and do not unnecessarily impact thenormal flow of user data in a detrimental fashion.

FIG. 2 illustrates a block diagram of a general communication system 200that includes a plurality of nodes 210-220 that are controlled by anetwork manager 205. The nodes 210-220 are intercoupled in a manner thatallows for data communication amongst the nodes included in the system200.

In one example, a connection may be established between endpoint A 241and endpoint B 242. Initially, data being transmitted from endpoint A241 to endpoint 242 may traverse the network by starting at node 210,traveling through nodes 212 and 214, and finally arriving at node 216.Assuming that the link 231 that connects nodes 212 and 214 is physicallysevered, conventional control plane and/or physical layer monitoringthat exists within the network will flag the failure such that a rerouteof the connection through nodes 218 and 220 is initiated. However, if aproblem arises along the initial connection that is not detectable usingthe control plane or physical layer monitoring that exits in prior artsystems, no such rerouting may occur and the user relying on theconnection to transfer data between endpoints A and B 241 and 242 may bedisappointed.

Thus, although the connection may appear fine from the perspective ofthe control plane and no problems may exist on the physical linkscoupling the various nodes included in the connection, other conditionsmay exist that cause a service interruption or degradation, such as astoppage or an unreasonable delay of data flow along the connection.Some specific examples may include a software fault (a specific card onone of the nodes is inadequately programmed), or a policingconfiguration that discards too much of the data included in the datastream traversing the connection, or switching fabric faults within anode.

Embodiments of the present invention ensure that such inadequacies alongthe connection that are not detectable based on conventional controlplane and physical layer monitoring are not left undetected. Byemploying a user connection monitoring function within the system, alack of continuity or an inadequate level of performance along theconnection can be detected such that a reroute or other correctiveaction is triggered in a similar manner as would occur if a signalinglink failure or physical link failure were detected, in order to restorean acceptable level of service.

In order to accomplish the user plane monitoring function, the sourcenode, in this case node 210, may inject diagnostic traffic into thestandard user data stream. In a particular example, the node 210 mayinclude an OAM cell source, where the OAM cells may be OAM CC cells orOAM PM cells. In other embodiments, similar diagnostic traffic may beinjected into data streams corresponding to protocols other than ATM.The destination node, in this case node 216, monitors the diagnostictraffic in the data stream in order to detect problems that exist alongthe connection as viewed from a user perspective. In the case where thesource node includes an OAM source, the destination node may include anOAM sink which extracts the OAM cells, and in the case of performancemonitoring cells, analyzes their receipt and content to determine theperformance of the connection.

Based on the status of the selected characteristics monitored throughthe user connection monitoring function, control plane rerouting can beinitiated such that a second connection is established between thesource node and the destination node when the performance of the initialconnection is unacceptable. Note that the monitoring function can beused to monitor data flow in both directions with respect to aconnection. Each endpoint of the connection may include a source andsink in order to verify continuity along the connection such that thereroute (or other corrective action) is triggered when a loss ofcontinuity is detected. In other embodiments, the reroute may betriggered by inadequate performance along the connection, where suchinadequate performance may include an unacceptable latency along theconnection, unacceptable cell loss, etc.

The determination that unacceptable performance exists along the initialconnection may be based on one or more predetermined thresholdsassociated with the various characteristics. This was described abovewith respect to FIG. 1. Furthermore, the reroutes initiated may includesoft or hard reroutes, where the determination as to which type ofreroute to perform may be based on the unacceptable condition thatexists on the initial connection.

FIG. 3 illustrates a network 300 that includes a plurality of nodes 310,320, 330, and 340, where the network 300 is managed by a network manager350. In the case where the network 300 supports ATM functionality suchthat the various nodes 310, 320, 330, and 340 are ATM nodes, orswitches, the specific connections supported may include SPVC's. In sucha network, the techniques described herein may allow the network torecover from many types of data flow interruptions on the SPVC paths byinitiating a reroute when such data flow interruptions are detected.Such added functionality increases the robustness of the SPVC's, whichmay help to provide the level of service expected by subscribers who payfor such SPVC services.

In order to detect the data flow interruptions, OAM CC cells may beutilized within the network 300. Assuming that the nodes 310 and 340serve as source and destination nodes, respectively, for a connectionthat also utilizes nodes 320 and 330, the nodes 310 and 340 may includeuser network interface (UNI) ports 312 and 342, respectively. The UNIports 312 and 342 may provide the connection points for customerpremises equipment (CPE). The endpoint nodes 310 and 340 may alsoinclude network-to-network interface (NNI) ports 314 and 344,respectively, that couple the endpoint nodes to the other nodes withinthe network. As such, in various embodiments the monitoring function maybe performed either at UNI ports or NNI ports, and the monitoring can beused to help maintain NMS PVCs or SPVCs.

In order to support rerouting of SPVC's based on the determination thata lack of continuity condition exists, OAM CC source and sink points maybe enabled at the NNI or UNI portions 314 and 344 of the endpoint nodes310 and 340, respectively. Both the source and destination nodes 310 and340 should be capable of running OAM CC and also capable of serving asSPVC endpoints. However, no such requirement exists for the intermediatenodes 320 and 330 that may exist along the connection. Furthermore, nospecialized functionality is required by intermediate nodes along thepath in order to ensure that continuity exists along the connection, aswell known OAM CC functionality is capable of ascertaining whether ornot a lack of continuity condition exists.

Although a portion of the SPVC path between the UNI and NNI cards on thesource and destination nodes is not monitored for continuityverification, it may be preferable to establish the OAM CC source andsink points on the NNI cards 314 and 344 for other reasons. A firstreason is that SPVCs may originate or terminate on UNI cards that do notsupport OAM CC, and as such, attempting to establish source and sinkpoints to ensure continuity at such UNI cards would fail and defeat theuser plane monitoring functionality desired. Secondly, if OAM CC is runbetween the UNI cards, physical removal or reset of the UNI card ateither the source or destination node may cause the SPVCs originating orterminating at that UNI card to be rerouted repeatedly until the UNIcard becomes functional. Such a condition is highly undesirable as itwastes network resources.

In specific operation, the network manager 350 creates the initial SPVCpath definition and enables the SPVC rerouting on a loss of continuitycondition for the SPVC path defined. Such functionality within thenetwork manager 350 may be controlled through a graphical user interfaceby an operator of the network manager 350. Following the pathdefinition, the network manager 350 sets up the SPVC and establishes theOAM CC segment source and sinks at the NNI cards 314 and 344. Onceestablished, the OAM CC continues to run between the NNI's. Note that inother embodiments, the sources and sinks may be set up at UNIinterfaces. As such, the description provided with respect to NNI-NNImonitoring can easily be extrapolated to understand the UNI-UNI case.

When the NNI card at either the source or destination detects loss ofcontinuity on the SPVC path, it may send a message to a call processingentity with the indication that a loss of continuity has been detected.In the case of SPVC's, rerouting may be performed without theintervention of the network manager 350. As such, the call processingentity within the node that detects the loss of continuity may cause theSPVC to be released. Such release may include the communication of acause code that includes diagnostic information such that the loss ofcontinuity detection can be pinpointed to either the source ordestination node. Once this has occurred, the call processing entity atthe source node can reestablish an SPVC path, where such reestablishmentmay utilize standard routing procedures such that no special effort maybe made to avoid the previous path. In other embodiments, the nodesincluded in the original path or the likely location of the problemcausing the lack of continuity may be taken into account when thererouting occurs.

As is apparent to one of ordinary skill in the art, rerouting based on aloss of continuity detected for an SPVC path may be undesirable in somenetwork applications. As such, it may be desirable to allow suchrerouting based on loss of continuity to be toggled on and off forspecific SPVCs, or for various portions of the network in general.Furthermore, additional configurability may be achieved if rerouting ofSPVC's is also enabled based on substandard performance on a particularSPVC, where the performance may be monitored using OAM PM cells.

Generally, the present invention provides a method and apparatus forrerouting connections in a data communication network based on thedetection of faults in the connection based on a user plane monitoringtechnique. When such faults are detected in the connection, a reroute ofthe connection is triggered based on the fault that is detected. Asindicated herein, such faults may include loss of continuity orsubstandard performance for parameters typically associated with cell orpacket traffic in a communication network.

By enabling the traffic along a connection to be monitored from a userperspective using diagnostic traffic such as OAM cells, problems alongthe connection that may not have been detected with prior art monitoringtechniques may be readily ascertained such that reroutes can betriggered and adequate data flow ensured. As described herein, theapplicability of such monitoring techniques extend beyond ATM networks,and are readily applied to other protocols such as MPLS wheresubstandard performance along an LSP may be used to trigger such areroute condition.

In the foregoing specification, the invention has been described withreference to specific embodiments. However, one of ordinary skill in theart appreciates that various modifications and changes can be madewithout departing from the scope of the present invention as set forthin the claims below. Accordingly, the specification and figures are tobe regarded in an illustrative rather than a restrictive sense, and allsuch modifications are intended to be included within the scope ofpresent invention.

Benefits, other advantages, and solutions to problems have beendescribed above with regard to specific embodiments. However, thebenefits, advantages, solutions to problems, and any element(s) that maycause any benefit, advantage, or solution to occur or become morepronounced are not to be construed as a critical, required, or essentialfeature or element of any or all the claims. As used herein, the terms“comprises,” “comprising,” or any other variation thereof, are intendedto cover a non-exclusive inclusion, such that a process, method,article, or apparatus that comprises a list of elements does not includeonly those elements but may include other elements not expressly listedor inherent to such process, method, article, or apparatus.

1. A method for rerouting a connection in a data communication network,comprising: establishing the connection in the data communicationnetwork, wherein the connection is managed by a control plane;monitoring status of a selected characteristic of the connection using auser connection monitoring function; and when the status of the selectedcharacteristic is determined to be unacceptable, initiating controlplane rerouting of the connection, wherein the user connectionmonitoring function includes OAM continuity checking, wherein initiatingcontrol plane rerouting of the connection comprises evaluating a newconnection before the connection is abandoned, wherein the control planererouting over the new connection occurs when a new connection selectedcharacteristic of the new connection is better than the selectedcharacteristic of the connection.
 2. The method of claim 1, wherein theselected characteristic includes continuity on the connection.
 3. Themethod of claim 1, wherein the selected characteristic includes at leastone of: data corruption on the connection, data loss on the connection,latency along the connection, and misinsertion of data on theconnection.
 4. The method of claim 1, wherein the data communicationnetwork supports asynchronous transfer mode (ATM) protocol.
 5. Themethod of claim 4, wherein the control plane is a signaling plane. 6.The method of claim 5, wherein the signaling plane uses privatenetwork-to-network interface (PNNI).
 7. The method of claim 6, whereinthe connection is a soft permanent virtual connection (SPVC).
 8. Themethod of claim 6, wherein the connection is a switched connection. 9.The method of claim 8, wherein the user connection monitoring functionutilizes operation and management (OAM) traffic.
 10. The method of claim9, wherein the user connection monitoring function includes OAMperformance monitoring.
 11. The method of claim 10, wherein determiningthat the status of the selected characteristic is unacceptable furthercomprises determining that a property of the selected characteristicexceeds a predetermined threshold.
 12. The method of claim 11, whereinthe selected characteristic further comprises a plurality of selectedcharacteristics, wherein each selected characteristic of the pluralityof selected characteristics has a corresponding predetermined threshold,wherein determining that the status of the selected characteristic isunacceptable includes determining that a property corresponding to atleast one selected characteristic of the plurality of selectedcharacteristics exceeds the corresponding predetermined threshold forthe at least one selected characteristics.
 13. The method of claim 12,wherein at least a portion of the corresponding predetermined thresholdsfor the plurality of selected characteristics is configurable.
 14. Themethod of claim 1, wherein the data communication network supportsMulti-Protocol Label Switching (MPLS).
 15. The method of claim 14,wherein the control plane includes at least one of Label DistributionProtocol (LDP) and ReSerVation Protocol (RSVP).
 16. The method of claim14, wherein the connection is a Label Switched Path (LSP).
 17. Themethod of claim 16, wherein the user connection monitoring functionmonitors continuity along the connection.
 18. The method of claim 16,wherein the user connection monitoring function monitors at least oneof: data corruption on the connection, data loss on the connection,latency along the connection, and misinsertion of data on theconnection.
 19. The method of claim 1 wherein, when the status of theselected characteristic is determined to be unacceptable, the connectionstill appears fine from the perspective of the control plane.
 20. Themethod of claim 1 wherein, when the status of the selectedcharacteristic is determined to be unacceptable, the status of theselected characteristic determined to be unacceptable is not detectableusing control plane monitoring.
 21. The method of claim 1 wherein, whenthe status of the selected characteristic is determined to beunacceptable, the status of the selected characteristic determined to beunacceptable is not detectable using physical layer monitoring.
 22. Themethod of claim 1 wherein, when the status of the selectedcharacteristic is determined to be unacceptable, the status of theselected characteristic determined to be unacceptable is caused by asoftware fault.
 23. The method of claim 1 wherein, when the status ofthe selected characteristic is determined to be unacceptable, the statusof the selected characteristic determined to be unacceptable is causedby a policing configuration that discards too much of data included in adata stream traversing the connection.
 24. The method of claim 1wherein, when the status of the selected characteristic is determined tobe unacceptable, the status of the selected characteristic determined tobe unacceptable is caused by a switching fabric faults within a node.25. A data communication network, comprising: a source node; adestination node operably coupled to the source node via a firstconnection that carries a data stream, wherein the source node injectsdiagnostic traffic into the data stream, wherein the destination nodemonitors the diagnostic traffic in the data stream; and a control blockoperably coupled to the source node and the destination node, whereinwhen status of a selected characteristic associated with the diagnostictraffic is determined to be unacceptable, the control block performs acontrol plane reroute that establishes a second connection that couplesthe source node and the destination node, wherein the diagnostic trafficincludes operation and management (OAM) performance monitoring traffic,wherein the diagnostic traffic verifies that a level of user planeperformance that has been guaranteed to a user is being provided,wherein the control block performs an evaluation of the secondconnection, wherein the data stream is rerouted over the secondconnection only if a second connection status of the second connectionselected characteristic is better than the status of the selectedcharacteristic.
 26. The data communication network of claim 25, whereinthe data stream includes a plurality of asynchronous transfer mode (ATM)cells.
 27. The data communication network of claim 25, wherein thediagnostic traffic includes operation and management (OAM) continuitychecking traffic.
 28. The data communication network of claim 27,wherein the status of the selected characteristic is determined to beunacceptable when loss of continuity is detected for a time period thatexceeds a predetermined threshold.
 29. The data communication network ofclaim 25, wherein the status of the selected characteristic isdetermined to be unacceptable when a property associated with OAMperformance monitoring exceeds a predetermined threshold.
 30. The datacommunication network of claim 29, wherein the predetermined thresholdis configurable.
 31. The data communication network of claim 25, whereinthe first and second connections are soft permanent virtual circuits.32. The data communication network of claim 25, wherein the first andsecond connections are switched connections.
 33. The data communicationnetwork of claim 25, wherein the data stream is a Multi-Protocol LabelSwitching (MPLS) data stream and wherein the first and secondconnections correspond to label switched paths.
 34. The datacommunication network of claim 25, wherein the selected characteristicincludes at least one of: data corruption on the first connection, dataloss on the first connection, latency along the first connection, andmisinsertion of data on the first connection.
 35. A method for reroutinga connection in a data communication network, comprising: establishingthe connection in the data communication network, wherein the connectionis managed by a control plane; using operation and management (OAM)cells to monitor at least one characteristic of the connection; and whenstatus of the at least one characteristic is determined to beunacceptable, initiating control plane rerouting of the connection,wherein the OAM traffic comprises OAM continuity checking traffic,wherein the at least one characteristic includes continuity, wherein thecontrol plane rerouting of the connection comprises evaluating a newconnection such that rerouting to the new connection occurs when atleast one new connection-characteristic of the new connection is betterthan the at least one characteristic of the connection.
 36. The methodof claim 35, wherein the connection is a soft permanent virtualconnection (SPVC).
 37. The method of claim 35, wherein the connection isswitched virtual connection (SVC).
 38. The method of claim 35, whereinthe control plane is a signaling plane.
 39. The method of claim 38,wherein the signaling plane uses private network-to-network interface(PNNI).